CVE-2021-40985Public exploit

Converter crash via negative colormap index

Published Nov 3, 2021 · Updated Aug 4, 2024

Stack buffer under-read in HTMLDOC before 1.9.12 allows attackers to crash the converter through a crafted BMP image. The image_load_bmp function treats an EOF return from getc as a negative colormap index, reading one byte before the stack buffer. Exploitation requires a user to direct HTMLDOC to convert attacker-controlled HTML that references the malformed BMP, terminating the conversion process.

CVSS severity5.5
Medium
EPSS probability0.94%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stack buffer under-read in HTMLDOC before 1.9.12 allows attackers to crash the converter through a crafted BMP image. The image_load_bmp function treats an EOF return from getc as a negative colormap index, reading one byte before the stack buffer. Exploitation requires a user to direct HTMLDOC to convert attacker-controlled HTML that references the malformed BMP, terminating the conversion process.

The record

CVE
CVE-2021-40985
Published
Nov 3, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-125, T1204.002
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 3, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:P
5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-125Out-of-bounds Read
T1204.002User Execution: Malicious File

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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